Factors governing Yb magnetism in Yb_0.95PtIn₂ and other MgCuAl₂-type structures

The ternary compound YbPtIn₂ has been synthesized and its crystal structure determined using single crystal X-ray diffraction techniques. The compound crystallizes in the MgCuAl₂ structure, a ternary structure type often formed when rare earth metals, Group 10 transition metals, and indium are present in a 1:1:2 ratio. The unit cell is C-centered orthorhombic, space group Cmcm (#63) with lattice parameters of a=4.3410(1) Å, b=10.3230(2) Å, and c=7.8510(2) Å. Evidence is found for a substantial non-stoichiometry on the Yb site, in contrast to the Pt and In sites which behave as expected, and it is believed that the stoichiometry of this compound is more properly described as Yb_0.95PtIn₂. Magnetic and resistivity measurements reveal that YbPtIn₂ is a weakly interacting, non-magnetic metal exclusively containing Yb²⁺, and with a resistivity (ρ) varying from 34 μΩ cm at room temperature to a residual resistivity ρ₀ of 23 μΩ cm at 1.8 K. Density functional theory calculations suggest that the observed diamagnetic Yb behavior is expected for this compound, but that certain substitutions on the Pt or In site could help stabilize magnetic Yb³⁺ and potentially induce heavy fermion behavior.